Known light-based tracking systems are based on the broadcasting of a unique light identification information item (LID), which can be received and detected by means of a mobile communication unit. For this purpose, the LID is modulated on to the light stream in a manner which is invisible to the human eye. In order to detect the modulated signal with a mobile communication unit, there must be a visual connection (line of sight) between the mobile communication unit and the modulating light source. After reception, the LID is filtered out of the light and demodulated. The LID can itself contain a position information item; however, it can also be provided that the mobile communication unit sends the demodulated LID to a central control unit, which there determines a position specification associated with the LID using a look-up table and transmits it back to the mobile communication unit. The association between LIDs and position information items is stored in the central control unit in advance. In addition to the position information item, any desired additional metadata can be associated with the LID. In addition to the implementation mentioned, in which the look-up table is stored in an external central control unit, the look-up table can also be stored as an integrated part in an application which runs on the mobile communication unit, however. Conversely, the look-up table can also include dynamic information, such as which mobile communication unit has queried which position information item. This allows a dynamic motion profile to be recorded (tracking) and saved with a time stamp (tracing). This motion information can form the basis for a wide range of location-based services and analyses.
This known procedure only works, however, for as long as a line of sight exists between the mobile communication unit and the light source broadcasting the LID. If, for example, a mobile phone is used as a mobile communication unit and after the position query the person using it, the carrier, puts it back into a pocket, for example a trouser pocket, a jacket pocket or a handbag, while a positioning information item is indeed received and can be stored in the system, it can no longer be subsequently determined how the carrier of the mobile communication unit has later changed his position in the room.
Alternatively, there are different wireless radio-based systems, such as WLAN or Bluetooth. With these methods, the position of the transmitter, for example a WLAN Access Point WAC or iBeacon, is known and on the basis of the signal field strength of the received signal (Received Signal Strength, RSSI) the distance between the transmitter and the mobile communication unit can be estimated. In accordance with the rules of trilateration, for a unique positioning at least three different transmission sources are required.
In comparison to a light-based indoor navigation a number of disadvantages are found: on the one hand, a sufficiently large number of radio transmission sources must be installed. In contrast to this, the number of the light sources which are normally already present for lighting is already sufficient. For the required radio transmission sources a source of power must be ensured. In the case of WAC, a mains power supply is required. In the case of iBeacons with lower power consumption, batteries are required, all of which will correspondingly need to be replaced within one year. In contrast to this, during the installation of the lighting a mains power supply is always already available. Finally, in the case of radio-based indoor position solutions an accuracy of only 5 m to 10 m is obtained. In contrast, light-based systems can achieve an accuracy of up to less than 10 cm.
In summary, it can be stated that only the high accuracy of light-based systems allows the capability of tracking mobile receivers, and thus also the carriers of such systems, for example, persons, machines, robots, sufficiently precisely, to enable, for example, location-based services and analyses with high reliability.